Method for curing room-temperaturevulcanizing organopolysiloxane rubber



United States Patent Ofi ice 3,184,427 Patented May 18, 1965 Thisinvention relates to a method for curing roomtemperature-vulcanizingorganopolysiloxane rubber in relatively deep sections and to the heatstable compositions so formed.

In the field of silicone rubber, based primarily ondiorganopolysiloxanes, much Work has been done in developing rubberswhich vulcanize and cure at room temperature by the interaction ofchosen ingredients. One of these systems employs diorganopolysiloxanesendblocked with silicon-bonded oxime radicals. This system is disclosedin the copending application of Edward Sweet, Serial No. 132,555, filedAugust 21, 1961, now abandoned, entitled Silicone Intermediates, whichis hereby incorporated by reference. One of the advantages of thisparticular system is the fact that the product adheres well to anysurface in contact during the cure. However, this system does not curewell in thick or deep section, i.e., films thicker than about inch, orin confined spaces, Another disadvantage of this system is its poor heatstability when cured in semi-confined spaces, i.e., poor confined heatstability.

One of the objects of this invention is to provide a room temperaturecuring system similar to that identified above which will curesatisfactorily in deep section or in confined spaces. provide such asystem which has improved confined heat stability over similarpreviously known systems. A third object of this invention is to providea system having the above advantages without sacrificing the excellentbonding properties which are characteristic of the oxime system. Theseobjects are satisfied by this invention.

v This invention resides in a method comprising reacting (A) ahydroxy-endblocked silioxane composed of units of the formula :a'..s1o T(B) a silane of the formula R Si(ON'-=X) in an amount such that there isat least one ON=X radical per silicon-bonded hydroxyl group in siloxane(A), (C) a carboxylic acid anhydride of the general formula AcOAc in anamount such that there are at least .66 mol of the carboxylic acidanhydride per ON=X radical in the silane (B) and (D) magnesium oxide inan amount such that there is at least .33 mol of oxide (D) per ON=Xradical in the silane (B), in which components X is selected from thegroup consisting of radicals of the formula R C= and in which each R isselected from the group consisting of divalent hydrocarbon radicals andhalogenated divalent hydrocarbon radicals, each R being a radicalselected independently from the group consisting of monovalenthydrocarbon radicals and halogenated monovalent hydrocarbon radicalseach R is a substituent selected independently from the group consistingof R radicals, cyanoalkyl radicals and hydrogen atoms, a has a value offrom 1.9 to 2.1 inclusive, b has a value of from to 1 inclusive and Acis a saturated aliphatic monoacyl radical derived from a carboxylic acidof at least 2 carbon atoms.

Another object of this invention is to r The operative silanes are ofthe general formula R' Si(ON=X) The subscript b has a value of from 0 to1 inclusive. Thus, these silanes include and Si(ON=X) The method forpreparing these oxime silanes is disclosed in the copending Sweetapplication. This method generally involves the reaction of an oximewith a halogenosilane in the presence of an acid acceptor.

For the purpose of this invention X is either a radical of the formula RC= or R" can be any divalent hydrocarbon radical or divalenthalohydroearbon radical in which the two valences are attached to the Cof the C=NO group. Thus, for example, R" can be dHu mncm. utwumcm,

I cn on-onomc m, dmonorncrndm,

arena. aroma.

and

R and R can be any monovalent hydrocarbon radical or any halogenatedmonovalent hydrocarbon radical. More specifically R and R can be, forexample, any alkyl radical such as the methyl, ethyl, isopropyl,tert-butyl, 2- ethylhexyl, dodecyl, 1-isobutyl-3,S-dimethylhexyl,octadecyl and myricyl radicals; any alkenyl radical such as the vinyl,allyl, decenyl and hexadienyl radicals; any cycloalkyl radical such asthe cyclopentyl and cyclohexyl radi cals; any cycloalkenyl radical suchas the cyclopentenyl, cyclohexenyl and cyclo-2,4-hexadienyl radicals;any aryl radical such as the phenyl, naphthyl and xenyl radicals; anyaralkyl radical such as the benzyl, phenylethyl and xylyl radicals andany alkaryl radical such as the tolyl and dimethylphenyl radicals. Thesemonovalent hydrocarbon radicals can be halogenated to give such radicalsas the chloromethyl, 3,3,3 trifluoropropyl, 3,3,4,4,5,5,5heptafluoropentyl, perchlorophenyl, 3,4-dibromocyclohexyl, a, u,x-trifiuorotolyl, 2,4-dibromobenzyl, difiuoromonochlorovinyl,u,B,B-trifluoro-ot-chlorocyclobutyl and 2-idocycl0- penten-3-y1radicals, all of which are operative.

In addition, R can be any cyanoalkyl radical such as thebeta-cyanoethyl, gamma-cyanopropyl, omega-cyanobutyl, beta-cyanopropyl,gamma-cyanobutyl and omegacyanooctadecyl radicals. When cyanoalkylradicals are present, it is preferred that they be attached to at least1 mol percent of the silicon atoms in the compounds of this invention.Silanes of the formula RSi(ON=X) are preferred.

It is preferred that X is a R C: radical and that R and R are monovalenthydrocarbon radicals. Aliphatic hydrocarbon radicals of from 1 to 6inclusive carbon atoms are the preferred monovalent hydrocarbonradicals. The preis preferred.

The hydroxy-endblocked siloxane reactant is composed of units of theformula R'..sio

The polymer size of this hydroxy-endblocked siloxane can 7 vary fromthin fluids (e.g., Where there are five 2 V V units) to non-flowing gums(e.g., where there are 10,000 or more R .s1o

units) For the purpose of this invention, mixtures of hydroxy-endblockedsiloxanes can be employed which contain molecular species of varyingnumbers of 1 R.Si

units. Various types of R groups, which have been defined above, canappear in any one molecule. Thesiloxane can be a homopolymer or it canbe a copolymer of two or more different siloxane units.' Mixtures oftwoor more hydroxy-endblocked silanes can be employed. Often in actualcommercial operation the siloxane employed will be a mixture of severalmolecular species of varying mo-Q lecular weights. A pure species wheresome of the molecules have the same degree of polymerization can also beused. It is also preferred that the R groups in the by:

radical with the preferred monovalent hydrocarbon radicals beingaliphatic hydrocarbon radicals of from 1 to 6 inclusive carbon atoms.The subscript a has a value of from 1.9 to 2.1 inclusive.

While this invention involves primarily the reactionof ahydroxy-endblocked diorganosiloxanelA), an oximesilane (B), a carboxylicacid anhydride (C) and magnesium oxide (D), the invention involvesmodifications of thisreaction. One such modification involves the substi-tution of an oxime-endblocked diorganosiloxane. for

the oximesilane (B). This oxime-endblocked diorganoscripts 41,12 and chave the values stated above. The sum of b-l-c is 3. Preferably, b is 2.It is essential when this oxime-containing siloxane is used, that thereaction take place in the presence of moisture.

When a hydroxy-endblocked diorganopolysiloxane is used in combinationwith either an oximesilane or an oxime-endblocked siloxane, it isessential that there be at least. .66 mol of the carboxylic acidanhydride per ON=X radical and .33 mol ofmagnesium oxide per ON=Xradical in the composition. When a hydroxy-endbl'ocked siloxane is usedin combination with either an oximesilane or an oxime-endblockedsiloxane in an amount so that there are more than 1.5 oxime radicals persilicon-bonded hydroxyl radical,.it is preferred that the reaction takeplace in the presence of moisture.

While it is necessary'thatthere' be at least one. siliconbonded oxime(ON=X) radical per silicon-bonded hy- V droxyl radical when ahydroxy-endblocked siloxane is droxy-endblocked siloxane be a monovalenthydrocarbon ii used in combination with either'an oximesilane or oxime--endblocked siloxane, it is preferable that there be at least a 100percent molar-excess of oxime radicals. Similarly,

while a large molar excess,'e.g., a 20 fold excess of silicon-. bondedoxime radicals can be present, it is preferable that no more than a1,000 percent molar excess be present in the. initial reactants. Itshould be understood, however, that the method of this invention-isoperative with more than 1,000 percent molar excess of silicon-bondedoxime radicals over silicon-bonded hydroxyl radicals in the re actantsif desired. It should berpointed out that a ratio of one oxime radicalper hydroxyl radical is obtained when .33 mol of the oximesilaneRSi(ON=X) is used per mol of silicon-bonded hydroxyl groups in thesiloxane. It is preferred that either the oximesilane oroxime-endblocked siloxane be used in approximately equimolar ratio withthe 'hydroxy-endblo'cked siloxane.

When a hydroxy-endlocked diorganosiloxane is reacted with eitheranoximesilane or an oxime-end'blocked siloxane, it isessential thatthere 'be at least .66 mol oflcarboxylic acid anhydride per ON=X groupin the reactants. It is preferred that there beat least 1 mol of theanhydride per ON=X in the reactants. When only the oximesiloxsiloxane isof the general formula V ane is used, it is essential that there be atleast .66 mol ofthe carboxylic acid anhydride per oxime radical. The

oximesiloxane only .cures in the presence of moisture.

The carboxylic acid anhydrides are of the general formula AcOAc whereinAc is a saturated aliphatic monoacyl radical derived from'a oarboxylicacid of at least 2 carbon atoms. It is preferred thatthe Acradicalcontain from .2 to 6 inclusive carbon atoms. It is preferable toemploy at least a 2 fold excess of the carboxylic acid anhydride toinsure even and thorough dispersion of this ingredient in the system.However, a 10 fold excess or more of the X'and R'radicals and theirpreferred definitions are the i same as set forth above for the reactionof the oximesilane (B) and the hydroXy-endblocked siloxane (A). This.oxime-endblocked siloxane can be produced by the re- (A) and theoximesilane. (B);

Another modification involves thesubstitutionfof an.

oxime-containing diorganosiloxane .for both the hydroxy endblocked,diorganosiloxane (A) and the oximesilane (B). This oxime-containingdiorganosiloxane consists essentially of at least 2 units of the generalformula (X=NO)SiR O with any other units in said siloxane having thegeneral anhydride .can be employed, if desired, without affecting thecure mechanism of the system. Suitable examples of carboxylicacid'anhydrides are acetic anhydride, isobutyric anhydride, hexoic'anhydride, Z-ethylhexoic anhydride, octanoic anhydride, stearicanhydride and acetic butyric anhydride. Acetic anhydride is preferred.

In addition to the carboxylic acid anhydride, it is also essentialthat.there be 'atleast133 mol of magnesium oxide per ON=X radical in theoximesilane when the oximesilane andhydroxy-endblocked siloxanes arereacted. It is preferredthat there be .5 mol of magnesium oxideper ON=Xradical in the .oximesilane (e.g., 1.5 mols of oxide per molof R'Si(ON=X) 'si1ane). When the hydroxy-endblocked diorganosiloxa'ne andoxime-endblocked siloxane are reacted, it is necessary that there be atlcast .33 mol of magnesium oxide per X=NO radical in the reactants. .Itis preferred that there be at least .5 mol ofoxide per X=NO radical.When only the oximesiloxane is'used, it is essential that there be .33mol of oxide per X--NO radical andpreferred that there is at least .5mol of magnesium oxide. It is preferable to employ at least a 2 foldexcess of magnesium oxide to insure even and thorough dispersion of thisingredient in the system. It is preferred that there be at least .5 molof oxide per mol of carboxylic acid anhydride.

The method of this invention operates spontaneously upon the mixing ofthe named reactants to produce a cured rubber. Temperatures ranging fromC. to 100 C. are sufficient although higher or lower temperatures can beemployed depending only on the freezing point, boiling point ordecomposition temperature of any reactant. The rate of cure can beslowed by increasing the size of the R and R radicals in theorganosilicon compounds, by increasing the size of the oxime radical(ON=X) or by increasing the ratio of silicon-bonded oxime radicals tosilicon-bonded hydroxyl radicals. For commercial use the best method forpracticing this invention is to prepare two components, one componentcontaining the hydroxy-endblocked siloxane and the oximesilane oroximesiloxane containing the carboxylic acid anhydride. When only theoximesiloxane is used, it is necessary that the carboxylic acidanhydride be mixed with the siloxane just prior to curing. Thehydroxy-endblocked diorganosiloxane and oximesilane reactants arepreferred.

These components can be co-reacted at elevated temperatures, if desired,or in the presence of condensation catalysts.

Typical classes of such condensation catalysts include, for example,certain organic amines, phosphoric acid salts of any basic aminocompound, carboxylic acid salts of any basic amino compound, carboxylicacid salts of any quaternary ammonium hydroxide and carboxylic acidsalts of any metal ranging from lead to manganese inclusive in theelectromotive series of metals.

The physical properties of the compounds of this invention can bemodified by mixing therewith other types of siloxanes and/or fillers.For example, it may be desirable to increase the adhesive qualities ofthe compounds of this invention by mixing therewith resinous siloxanes.These resinous siloxanes will also modify the elastic properties of theultimate vulcanized compositions to make them more dough-like and lessresilient. Such properties are highly desirable in certain calkingapplications. It also may be desirable to plasticize the vulcanizedcompositions of this invention by incorporating therein certainunreactive hydroxyl-free siloxane plasticizing agents such astrimethylsiloxy-endblocked dimethylsiloxanes. Silica fillers areemployed in the compositions of this invention in an amount ranging fromabout 5 to 150 parts by weight based on 100 parts of thehydroxy-endblocked sil-oxane (A). When only an oximesiloxane is used,silica fillers can be employed in an amount ranging from about 5 to 160parts by weight based 011100 parts of the oximesiloxane.

The compounds of this invention can also be modified by incorporatingtherein any of the well-known reinforcing fillers such as fume silicas,silica aerogels and precipitated silicas of high surface area. Thesefillers, if desired, can have organosilyl groups attached to the surfacethereof. The fillers employed herein can also .be non-reinforcingfillers such as coarse silicas such as diatomaceous earth, crushedquartz or metallic oxides such as titania, ferric oxide, zinc oxide andthe like. If desired, fibrous fillers such as asbestos or glass may alsobe employed. In short, any of the fillers commonly employed withsilicone rubbers may be employed in the compositions of this invention.In all cases it is desirable that the filler be substantially dry beforeadmixing with the composition although some water can be tolerated if anexcess of the oximesilane is employed.

The fillers are usually employed to increase the strength of theelastomeric compositions and also to modify the flow characteristics ofthe uncured composition. The latter is particularly important in calkingapplications where it is undesirable to have any appreciable flow take 6place between the time the material is placed in the joint and the timecuring occurs.

In addition to the above ingredients the compositions of this inventioncan contain any other desirable additive such as pigments, sun-screenagents, oxidation inhibitors and dielectric materials such as graphiteand carbon black.

The following examples are illustrative and are not intended to limitthis invention the scope of which is properly delineated in the claims.All quantitative measurements are in parts by weight. All viscositieswere measured at 25 C.

EXAMPLE 1 Sample A was prepared by mixing parts by weight of a 12,500cs. hydroxyl-endblocked dimethylsiloxane with 40 parts by weight of a1,000 cs. trimethylsilyl-endblocked dimethylsiloxane, 13 parts by weightof a reinforcing fume silica and 10 parts by weight of (equivalent to 25ON=C(CH per hydroxyl radical). Sample B was prepared by mixing 100 g. ofSample A with 7.36 g. of acetic anhydride (equivalent to 1 mol of aceticanhydride per -ON=C(CH radical) and 1.25 g. of magnesium oxide(equivalent to .5 mol of magnesium oxide per ON=C(CH radical). Eachsample was then confined in a small cavity about /2 inch deep and 1 inchin diameter. Each sample was wrapped tightly in 1 mil aluminum foil toexclude atmospheric moisture and was allowed to stand for 24 hoursbefore checking the cure. Sample B was cured to the extent that it has aShore A durometer of 12 after 24 hours. Sample A was uncured after both24 hours and 7 days.

EXAMPLE 2 Sample A Was prepared by mixing parts by weight of ahydroxyl-containing dimethylsiloxane with a viscosity of about 12,000cs. with 14 parts by weight of a reinforcing fume silica, 4 parts byweight of a hydroxylendblocked phenylmethylsiloxane fluid and 10 partsby weight of (CH CH)Si[ON=C(CH CH (CH3) 1 (equivalent to more than 1ON=C(CH CH (CH radical per OH group). Sample B was identical with SampleA except that it also contains 7.36 parts by Weight acetic anhydride(equivalent to 1 mol anhydride per cure. The cure was also checked after7 days. Shore A durometer of each sample is set forth in Table I.

Table I Shore A Durometer Sample 1 day 7 days EXAMPLE 3 When any of thefollowing silanes are substituted mol per mol for the (CH )Si[ON=C(CH 1in Sample B of Example 1 and the procedure of Example 1 is followed,

an excellent room temperature vulcanizing rubber which [(CH C QN O] Si(CH5 OISi CH5 CH cures well in deep section is obtained:

Si[ON=(; (CHQslHzh Si[ 6 5) 3) ]4 EXAMPLE 4 When any of the followingcarboxylic acid anhydrides 7 HzCEa) ZO -(CHS) a)2] 2 .s)2 ]2 3) O K FJ ss That which is claimed is I V 1'. A. method comprising reacting (A) "ahydroxy -andblocked siloxane composed of units of the formula (B) and(D) magnesium oxide in an amount such that are substituted mol per molfor the acetic anhydride of a EXAMPLE 5 When any of the siloxanes of thefollowing unit formulae are substituted for the (CH )Si[ON=C(CH inSample B of Example 1' in an equimolar ratio with the'hydroXyl-endblocked dimethylsiloxane, an excellent room temperaturevulcanizing rubber which cures well in deep section is obtained: a

l( 3)2 ]2 3) sH5) EXAMPLE 6 there is at least .33 mol of oxide (D) perON=X radicals in silane (B), inwhichcomponents X is selected from thegroup consisting of radicals of the formula 11 C: and

in which each R" is selected from the group' consisting of divalenthydrocarbonradicals and halogenated divalent hydrocarbon radicals, eachR being a radical selected incarbonfatorns'.

dependently from the group consisting of monovalent hydrocarbon radicalsand halogenated monovalent hydrocarbon radicals, each R is a substituentselected independently from :the group'consisting of R radicals,cyanoalkyl radicals and hydrogen atomsyd has a value'of from 1.9

to 2.1 inclusive, b has'a value of from O to 1 inclusive,

and Ac is a saturated aliphatic monoacyl radical derived from acarboxylic 'acidof at least 2 carbonatoms. 21A method in accordancewithclaim 1 wherein X is a R C= radical, Rand R are monovalenthydrocarbon radicals and eachAc radical has from 2 to 6 inclusive 3. Amethod comprising reacting (A) a hydroxyendblocked siloxane composed ofunits of the formula v 2 V a (B) a silane of the formula RSi(ON=CR in anamount such that there is at least 0.33 mol of silane (B) persilicon-bonded hydroxyl group in siloxane (A),

When partsby'weight of any of the'siloxanes of p the following unitformulae are mixed with 40 parts by weight of a 1,000 cs. trimethylsilylendblocked dimethylsiloxane, 10 parts by weight of a reinforcing fumesilica and sufiicient acetic anhydride to provide 1 mol of the anhydrideper oxime radical in'the siloxane andsufiicient magnesium oxide toprovide at least .5 mol per oxime radical and a /2 inch deep section ofthe mixture is allowed to cure in the presence of moisture, a well-curedrubber is obtained:

[ Ha)2 su i Ha) (C 3)2]2 b blocked siloxane composed of units (C) acarboxylic acid anhydride of the general formula AcOAc so thatithere isat least 3 mols of the carboxylic acid anhydride per mol of silane (B)and (D) magnesium oxide in an amount such that there are at least 1.5mols of oxide (D) per mol of silane (B), in which components R and R arealiphatic hydrocarbon radicals of from 1 to 6 inclusive carbon atoms, Ac7 is a saturated aliphatic monoacyl radical derived from a carboxylicacid of from 2 to 6 inclusive carbon atoms and a has value of from 1.9to 2.1 inclusive.

4. A method comprising reacting (A) a hydroxyendof the formula in anamount such thatthere is at least 0.33 mol of silane (B) persilicon-bonded hydroxyl group in siloxane (A), (C) acetic anhydride'inan amount such that there are at least 3 mols of acetic anhydride permol of silane (B) and (D) magnesium oxidein an amount such that thereare at least1.5 mols of oxide ,(D) per mol of silane (B). a

5. A composition 'consistingessentiafly of the reaction product of (A) ahydroxy-endblocked-siloxane composed 9 (B). a silane of the formula RSi(ON=X) in an amount such that there is at least one ON=X radical persilicon-bonded hydroxyl group in siloxane (A), (C) a carboxylic acidanhydride of the general formula AcOAc in an amount such that there areat least .66 mol of the carboxylic acid anhydride per ON:X radical inthe silane (B) and (D) magnesium oxide in an amount such that there isat least .33 mol of oxide (D) per ON=X radical in silane (B), in whichcomponents X is selected from the group consisting of radicals of theformula R C: and

in which each R" is selected from the group consisting of divalenthydrocarbon radicals and halogenated divalent hydrocarbon radicals, eachR being a radical selected independently from the group consisting ofmonovalent hydrocarbon radicals and halogenated monovalent hydrocarbonradicals, each R is a substituent selected independently from the groupconsisting of R radicals, cyanoalkyl radicals and hydrogen atoms, a hasa value of from 1.9 to 2.1 inclusive, b has a value of from to 1inclusive and Ac is a saturated aliphatic monoacyl radical derived fromcarboxylic acid of at least 2 carbon atoms.

6. A composition in accordance with claim wherein X is a R C= radical, Rand R are monovalent hydrocarbon radicals and each Ac radical has from 2to 6 inclusive carbon atoms.

7. A composition consisting essentially of the reaction product of (A) ahydroxy-endblocked siloxane composed of units of the formula (B) asilane of the formula R'Si(ON=CR in an amount such that there is atleast 0.33 mol of silane (B) per silicon-bonded hydroxyl group insiloxane (A), (C) a carboxylic acid anhydride of the general formulaAcOAc so that there are at least 3 mols of the carboxylic acid anhydrideper mol of silane (B) and (D) magnesium oxide in an amount such thatthere are at least 1.5 mols of oxide (D) per mol of silane (B), in whichcomponents R and R are aliphatic hydrocarbon radicals of from 1 to 6inclusive carbon atoms, Ac is a saturated aliphatic monoacyl radicalderived from a carboxylic acid of from 2 to 6 inclusive carbon atoms anda has a value of from 1.9 to 2.1 inclusive.

8. A composition consisting essentially of the reaction product of (A) ahydroxy-endblocked siloxane composed of units of the formula (CH SiO,(B) a silane of the formula (CI-IFCH)Si[ON=C(CH )(CH CH in an amountsuch that there is at least 0.33 mol of silane (B) per silicon-bondedhydroxyl group in siloxane (A) and (C) acetic anhydride in an amountsuch that there are at least 3 mols of acetic anhydride per mol ofsilane (B) and (D) magnesium oxide in an amount such that there are atleast 1.5 mols of oxide (D) per mol of silane B). 9. The composition ofclaim 5 with from 5 to 150 parts by weight per 100 parts of (A) of asilica filler.

10. The composition of claim 6 with from 5 to 150 parts by weight per100 parts of (A) of a silica filler.

11. The composition of claim 7 with from 5 to 150 parts by weight per100 par-ts of (A) of a silica filler.

12. The composition of claim 8 with from 5 to 150 parts by weight per100 parts of (A) of a silica filler.

13. A method comprising reacting in the presence of moisture (A) anuncured siloxane compound, each molecule of which consists essentiallyof at least 2 units of the general formula any other units in saidsiloxane having the general formula (B) a carboxylic acid anhydride ofthe general formula AcOAc in an amount such that there is at least .66mol of the carboxylic acid anhydride (B) per XT -NO radical in (A) and(C) magnesium oxide in an amount such that there is at least .33 mol ofoxide (C) per X=NO radical in (A), in which components X is selectedfrom the group consisting of radicals of the formula R 0: and

in which each R" is selected from the group consisting of divalenthydrocarbon radicals and halogenated divalent hydrocarbon radicals, eachR is a radical selected from the group consisting of monovalenthydrocarbon radicals, each R is a substituent selected independentlyfrom the group consisting of R radicals, cyanolkyl radicals and hydrogenatoms, Ac is a saturated aliphatic monoacyl radical derived from acarboxylic acid of at least 2 carbon atoms, b has a value of from O to 1inclusive, 0 has a value of from 2 to 3 inclusive and a has a value offrom 1.9 to 2.1.

14. The method of claim 13 wherein X is a R C= radical, R and R aremonovalent hydrocarbon radicals and Ac has from 2 to 6 carbon atoms.

15. A method comprising reacting in the presence of moisture (A) anuncured siloxane compound, each molecule of which consists essentiallyof at least 2 units of the general formula (R C=NO) SiR'O any otherunits in said siloxane having the general formula R' SiO (B) acarboxylic acid anhydride of the general formula AcOAc in an amount sothat there is at least one mol of the carboxylic acid anhydride (B) perR C=NO radical in (A) and (C) magnesium oxide in an amount so that thereis at least .5 mol of oxide (C) per R C=NO radical in (A), in whichcomponents R and R are aliphatic hydrocarbon radicals of from 1 to 6inclusive carbon atoms and Ac is a saturated aliphatic monoacyl radicalderived from a carboxylic acid of from 2 to 6 inclusive carbon atoms.

16. A method comprising reacting in the presence of moisture (A) anuncured siloxane compound, each molecule of which consists essentiallyof at least 2 units of the general formula (CHFCH) [ON=C(CH (CH CH SiOany other units in said siloxane having the general formula (CH Si0, (B)acetic anhydride in an amount such that there is at least one mol ofacetic anhydride (B) per (CH C=NO radical in (A) and (C) magnesium oxidein an amount such that there is at least .5 mol of oxide (C) per (CHC==NO radical in (A).

17. A method comprising reacting (A) a hydroxyendblocked siloxanecomposed of units of the formula (B) a compound of the formula in asuflicient amount so that there is at least one X=NU radical persilicon-bonded hydroxyl radical in (A), (C) a carboxylic acid anhydrideof the general formula AcOAc in an amount such that there is at least.66 mol of the carboxylic acid anhydride (C) per X=NO radical in (B) and(D) magnesium oxide in an amount such that there is at least .33 mol ofoxide (D) per X==NO radical in (B), in which components X is selectedfrom the group H (D) mag nesium oxide in an amount so that there is atconsisting of radicals of the formula R C= and Rm: .Ll

in which each R" is selected from the group consisting of divalenthydrocarbon radicals and halogenated divalent hydrocarbon radicals, eachR is a radical selected from the group consisting of monovalenthydrocarbon radicals,

each R is a substituent selected independently from the,

group consisting of R radicals, cyanoalkyl radicals and hydrogen atoms,and Ac is'a saturated aliphatic mono! acyl radical derived from acarboxylic acid of at least 2 19. A method comprising reacting (A) ahydroxyendblockedsiloxane composed of units of the formula (B) acompound of the formula (R C =NO SiR'O [SiR O] SiR' (ON=CR 2 in anapproximately equimolar ratio with (A), (C) a carboxylic acid anhydrideof the general formula AcOAc in an amount so that there is at least 1mol of carboxylic acid anhydride (C) per R Q- -NO radical .in (B) andleast .5 mol of oxide (D) per R C=NO radical in (B), in which componentsRand R are aliphatic hydrocarbon radicals of from 1 to 6 inclusivecarbon atoms and Ac is a saturatedzaliphatic monoacyl radical derivedfrom a carboXylic acid .of from 2 to 6 inclusive carbon atoms, n is apositive integer of atleast 5 and a has a value of from 1.9 to 2.1inclusive. 7 a

20. A method comprising reacting (A) a hydroxyendblocked siloxanecomposed of units of the formula R',sio (B) a compoundof the formula[(CH CH (c c=No] si cH =cH o (C 3)z ]n z) I [ON=C( H3) 2 3) 12 in anapproximately equimolar ratio with (A), (C) acetic anhydride in anamount such that there is at least 1 mol of acetic anhydride (C) per (CHC -NO radical in (B) and (D) magnesium'oxidein an amount suchthat there.least 5 and a has a value of from L9 to 2.1 inclusive,

' References Cited bythe Examiner UNITED STATES PATENTS 2,938,010 5/60Bluestein 26046.5

MURRAY TlLLMAN, Rrimary Examiner.

7 WILLIAM H. SHORT, Examiner.

1. A METHOD COMPRISING REACTING (A) A HYDROXY-ENDBLOCKED SILOXANECOMPOSED OF UNITS OF THE FORMULA
 5. A COMPOSITION CONSISTING ESSENTIALLYOF THE REACTION PRODUCT OF (A) A HYDROXY-ENDBLOCKED SILOXANE COMPOSED OFUNITS OF THE FORMULA